1. Field of the Invention
The present invention relates to a plasma etching chamber for manufacturing semiconductor devices, and more particularly, to a plasma etching chamber wherein the plasma gas formed by the radio frequency (RF) energy is made uniform by stabilizing the magnetic field for guiding the plasma gas, thereby preventing the plasma from converging at any one portion in the chamber.
2. Description of the Related Art
A plasma etching process is a type of dry etch process performed during a semiconductor device fabrication process. A plasma etcher works by creating a high-energy plasma in highly reactive gases. These ionized molecules react on the wafer surfaces with the appropriate films in a controlled and predictable fashion.
A typical plasma etch process is carried out as follows. First, wafers to be etched are transferred to an etching chamber, the process chamber is evacuated to create a vacuum state therein, and then specific process gases are supplied to the etching chamber. Next, RF energy is applied to the etching chamber to thereby create the high energy plasma from the ionized molecules of the specific process gases. Finally, these ionized molecules react with the wafer surface to etch the surface thereof.
In order to provide a more uniform plasma to improve the etching uniformity, a magnetic field is formed inside the etching chamber for guiding the plasma gases to the wafer surface.
FIG. 1 shows a conventional plasma etching chamber. A plurality of magnet coils 12 are disposed on the outer wall of the etching chamber 10, and power is supplied to the magnet coils 12 via a power cable 14. A magnetic field M is formed inside the etching chamber 10 by the power applied to the magnet coil 12, with the magnetic field M being induced according to the electrical polarities of the elements constituting the process gas in the plasma state. As described above, the plasma gas is directed toward a wafer surface where it reacts with the material on the wafer surface to perform the etch process.
The power cable 14 is connected to a bracket 16 which is in turn attached to the etching chamber 10. A connection nut 18 is inserted at the coupling location between the bracket 16 and the power cable 14 so as to support and fix the power cable 14 to the bracket 16.
However, the conventional dry etch facility constructed as above causes "convergence" of the plasma within the etching chamber around the connection site between the bracket 16 and the chamber 10. The connection site (not shown) is referred to as the EPD (End Point Detection) window. The convergence is caused by a partial discharge around the bracket 16 where the power cable 14 is connected. The conventional bracket 16 is made of a conductive material, aluminum, which is hard anodized by an electrolysis process. The magnetic field M inside the etching chamber 10 is affected by this partial discharge, as indicated by the spike "S" as shown by the arrow in FIG. 1. This spike S results in a concentration of the plasma in a direction confronting the connection site. As a result, the distribution of the plasma gas becomes unbalanced, and the portion of the wafer where the plasma gas is concentrated is over-etched.
Moreover, the connection nut 18 does not adequately support the power cable 14 where it is connected to the bracket 16. Indeed, the power cable 14 sometimes becomes detached due to vertically applied stress and friction. The detachment of the power cable shuts down the etching apparatus and thus decreases the operational efficiency.